PROJECT SUMMARY/ABSTRACT Coronavirus disease 2019 (COVID-19) is an emerging global pandemic caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). COVID-19 is imposing a tremendous public health threat, with no vaccines and therapeutic agents against SARS-CoV-2 currently available. This novel single-stranded enveloped RNA virus is the seventh known human coronavirus. SARS-CoV-2 is unlike the other coronaviruses known to cause the common cold (229E, OC43, NL63, and HKU1), but similar to the zoonotic severe acute respiratory syndrome coronavirus from 2002 and the Middle East respiratory syndrome coronavirus from 2012. Pneumonia and respiratory failure are the reported clinical complications of the infected by these coronaviruses. While vaccines and monoclonal antibodies against SARS-CoV-2 are in development, a number of investigational therapies are currently being considered and tested, including repurposed clinically approved drugs targeting SARS-CoV-2 cell entry and replication. For example, viral polymerases have been major therapeutic targets, as seen in multiple drug discovery successes targeting various viral pathogens (e.g., HIV- 1, HCV, and HBV). In fact, the chemistry team of our Center for Drug Discovery (CDD) at Emory University (led by Dr. R. F. Schinazi), have previously discovered several nucleoside/nucleotide viral polymerase inhibitors including lamivudine (3TC) and emtricitabine (FTC) to treat HIV, as well as sofosbuvir to cure HCV. Building on this successful mechanistic strategy, our current strategic approach for SARS-CoV-2 is to target its viral RNA- dependent RNA polymerase with specific nucleoside compounds that could potentially inhibit viral replication. In this competitive revision application, we have chosen a highly selective and chemically diverse nucleoside/nucleotide RNA polymerase inhibitor library, which consists of 200 compounds. We have previously established a safe toxicity profile for this set of compounds using our in vitro toxicity screening assay that consists of a panel of key cell-lines including human primary cells. Our goal is to investigate the antiviral efficacy of each of these compounds by employing our established in vitro SARS-CoV-2 virus culture and viral assay system.